
package tij4.ch17;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;



	class CircularSet
	{
		private int[] array;
		private int len;
		private int index = 0;

		public CircularSet(int size)
		{
			array = new int[size];
			len = size;
			// Initialize to a value not produced
			// by the SerialNumberGenerator:
			for (int i = 0; i < size; i++)
				array[i] = -1;
		}

		public synchronized void add(int i)
		{
			array[index] = i;
			// Wrap index and write over old elements:
			index = ++index % len;
		}

		public synchronized boolean contains(int val)
		{
			//System.out.println(val + " with " + Thread.currentThread());
			for (int i = 0; i < len; i++)
				if (array[i] == val)
					return true;
			return false;
		}
	}

	public class SerialNumberChecker
	{
	
	private static final int SIZE = 1000;
	private static CircularSet serials =  new CircularSet(1000);
	
	private static ExecutorService exec = Executors.newCachedThreadPool();

	static class SerialChecker implements Runnable
	{
		public void run()
		{
			while (true)
			{
				int serial = SerialNumberGenerator.nextSerialNumber();
				if (serials.contains(serial))
				{
					System.out.println("Duplicate: " + serial);
					System.exit(0);
				}
				serials.add(serial);
			}
		}
	}

	public static void main(String[] args) throws Exception
	{
		for (int i = 0; i < SIZE; i++)
			exec.execute(new SerialChecker());
		// Stop after n seconds if there's an argument:
		if (args.length > 0)
		{
			TimeUnit.SECONDS.sleep(new Integer(args[0]));
			System.out.println("No duplicates detected");
			System.exit(0);
		}
	}

}
